<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>显示信息</title>
</head>
<body>
  <a onmouseover="appear();" onmouseout="disAppear();" style="color: blue" id="baidu" title="我是你哥" href="add-helf.html">百度</a>
  <div id="message"></div>
</body>
</html>
<script>
  function appear(){
    let message = document.getElementById("message");
    message.innerText = "百度一下你就知道了!"
  }
  function disAppear(){
    let message = document.getElementById("message");
    message.innerText = "";
  }
</script>